Spontaneous fission

Spontaneous fission is the splitting of a heavy atomic nucleus into two or more lighter nuclei without an incoming particle. It releases energy and usually emits neutrons.

Nuclear fission: The division of an atomic nucleus into lighter nuclei, often accompanied by emitted neutrons and energy. Spontaneous fission is the untriggered mode of this broader nuclear process.
Spontaneous fission half-life: The time required for half the nuclei in a sample to decay through spontaneous fission. It quantifies how likely a particular nuclide is to undergo this decay mode.
Induced fission: Nuclear fission initiated when a nucleus absorbs or interacts with an incoming particle or photon. Unlike spontaneous fission, this process requires an external trigger.
Californium-252: A radioactive isotope of californium that undergoes both alpha decay and spontaneous fission. Its spontaneous fission makes it a compact source of neutrons.
Quantum tunneling: A quantum process in which a particle or system crosses an energy barrier it could not cross classically. A nucleus can tunnel through the fission barrier even when it lacks enough energy to pass over it.
Nuclear forensics: The analysis of nuclear or radioactive materials to determine their origin, history, and intended use. Isotopic ratios and spontaneous-fission products can help characterize nuclear materials.
Alpha decay: Radioactive decay in which a nucleus emits a helium-4 nucleus. Alpha emission competes with spontaneous fission as a decay route for some heavy nuclides.
Uranium-238: A naturally occurring uranium isotope with a half-life of about 4.5 billion years. It can undergo spontaneous fission, though alpha decay is far more frequent.
Fission barrier: The energy barrier that resists deformation of a nucleus toward configurations that split into fragments. Its height and shape help determine the spontaneous-fission probability.
Neutron background: Unwanted neutron events that interfere with measurements in a detector or experiment. Spontaneous fission in actinides can supply neutrons that experiments must account for.

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